1. Field of the Invention
The present invention relates to a polyester film for a magnetic tape, more particularly to a polyester film suitable for a nonback-coated magnetic recording tape.
2. Description of Related Art
Since video players are quickly widespread, video tapes are increasingly consumed and their prices are decreased. The consumers seek an inexpensive and high-quality tape giving high image quality.
In order to achieve the high image quality, smoothness of a magnetic layer surface is generally increased. To this end, it is necessary to use a smooth base film. But, the smooth base film give a bad traveling property. The traveling property can be improved by providing a back coating layer. Since the back coating layer increases the production cost of the tape, it is sought to improve the traveling property without providing the back coating layer.
Instead of providing the back coating layer, it is proposed to use a base film which has opposite surfaces having different sliding properties and in which one surface for receiving a magnetic layer is smooth and the other is rough. But, this film can not be employed since the rough surface makes the magnetic layer surface rough, namely "roughness transcription" phenomenon arises. Although it is proposed to suppress the "roughness transcription" phenomenon by improving the film which has opposite surfaces having different sliding properties through the increase of an amount of contained particles near the rough surface, this causes new problems that productivity is low and a quality of the magnetic tape is poor due to the drop-off of particles.